1. Field of the Invention
The present invention generally relates to the construction and use of vascular catheters. More particularly, the invention relates to intravascular catheters having a work element within a distal housing, and a work element guiding structure.
2. Previous Art
Arteriosclerosis, also known as atherosclerosis, is a disease characterized by the deposition of a fat-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits can occur both in peripheral blood vessels that feed the limbs of the body and in coronary blood vessels that feed the heart. When deposits accumulate in localized regions of a blood vessel, the regions become "stenosed"; blood flow is restricted and the person's health is at serious risk.
Numerous approaches for restoring blood flow by reducing and removing stenotic deposits have been proposed. Balloon angioplasty, for example, uses a balloon-tipped catheter to dilate the stenosed region. Atherectomy procedures use a blade or other cutting element to sever and remove stenotic material. Laser angioplasty directs laser energy to ablate at least a portion of the stenotic material.
Of particular interest are atherectomy catheters in which a cutting blade advances past an opening at the distal end of a vascular catheter. The catheter exposes the opening to at least a portion of the stenotic material. The stenotic material extends through the opening where the cutting blade advances and severs the stenotic material. Typically, such cutting blades are circular and are rotated (or rotationally oscillated) and advanced simultaneously to effect the desired cutting.
Although such atherectomy catheters have enjoyed widespread success in both peripheral and coronary applications, certain design limitations persist. In small diameter catheters used in the coronary arteries, for example, very tight vascular bends are encountered. Typically, a guidewire is first inserted through the blood vessel and advanced along the lumen of the vessel until proximate to the stenosed region. The catheter slides over, and along, the guidewire until the catheter positions adjacent a stensosed region. Atherectomy catheters having rigid housings at their distal ends have difficulty inserting past tight vascular bends. The rigidity of the housing causes lateral displacement of the guidewire. Difficulties associated with guide wire movement and tight vascular bends are exacerbated by elongated housings which frequently collect severed stenotic material in a forward nosecone.
In an effort to enhance the maneuverability within the tortuous regions of the coronary arteries, atherectomy catheters having flexible cutter housings have been employed. Commonly assigned flexible housings take various forms, including a braid-reinforced polymeric structure and a slotted metal tubular structure.
Although flexible housings offer a significant improvement over comparably sized rigid cutter housings when employed in coronary arteries and other tortuous regions of the vascular system, they do present limitations. In particular, bending and flexing of the flexible housings inhibits axial advancement of the cutting blades within the housing. Also, bending of the housing sometimes causes an advancing cutting blade to undesirably extend outward from the window. Outward extension of the cutting blade may render the cutting blade inoperable or interfere with the housing and the guidewire. Such consequences prevent proper operation of the catheter by distorting the housing. Outwardly extending cutting blades are unwieldy and generally undesirable.
Efforts to overcome undesired extension of cutting blades continue. Reducing the width of the housing window prevents extension of the cutting blades. This modification, however, reduces the amount of stenotic material which can be removed in a single pass of the cutting blade through the housing.
Various related efforts manifest themselves in atherectomy catheters described in U.S. Pat. No. 4,926,858, issued May 22, 1990 to Gifford, III et al. entitled "ATHERECTOMY DEVICE FOR SEVERE OCCLUSIONS"; U.S. Pat. No. 4,979,951, issued Dec. 25, 1990, to Simpson, entitled "ATHERECTOMY DEVICE AND METHOD"; U.S. Pat. No. 5,047,040, issued Sep. 10, 1991, to Simpson et al. entitled "ATHERECTOMY DEVICE AND METHOD"; U.S. Pat. No. 5,084,010, issued Jan. 28, 1992, to Plaia et al., entitled "SYSTEM AND METHOD FOR CATHETER CONSTRUCTION"; and Re. U.S. Pat. No. 33,569, issued Apr. 9, 1991, to Gifford III et al. entitled "SINGLE LUMEN ATHERECTOMY CATHETER DEVICE". Of these, the U.S. Pat. Nos. 4,979,951 and Re. 33,569 patents describe catheters having distal housings in which a rotatable cutting blade receives a coaxial movable guidewire. Moveable guidewires generally do not securely hold the cutting blade within the housing. Additionally, in some devices, the guidewire itself may be severed by the cutting blade. Copending U.S. Pat. No. 5,250,059, issued Oct. 5, 1993 to Andreas et al., entitled "ATHERECTOMY CATHETER HAVING FLEXIBLE NOSE CONE" is commonly assigned to the assignee of the present application, and describes an atherectomy catheter having a flexible nose cone attached to the distal end of a cutter housing. A rotatable cutting blade is optionally received over a movable guidewire which passes through the nose cone, the housing and the cutting blade drive (torque) cable.
Placement of the cutting blade of an atherectomy catheter over a conventional movable guidewire has been proposed (See, U.S. Pat. Nos. 4,669,469, and Re. 33,569). Conventional guidewires could restrain the cutting blade within the cutter housing under some circumstances. Unfortunately, the guidewire itself will often be displaced as the atherectomy catheter is advanced over the guidewire.
Guidewire movement is due to the fine gauge (usually 0.007 inch) of the guide wire. Furthermore, since the guidewire is not fixed at its distal end, it does not necessarily conform to the specific distortions of the housing within a contorted blood vessel, and thus is not always efficient in guiding the cutter as it is advanced within the housing. Thus, movable guidewires cannot be relied on to cooperate with an axially translatable cutter within the cutter housing under all circumstances.
Improved intravascular catheters are desired. In particular, it is desirable to provide a way of retaining a cutting blade (work element) within the housing of a catheter. It is desirable to provide a flexible housing in which the cutting blade will not interfere with the guidewire or the housing of the catheter. It is desirable to provide a way of retaining the cutting blade which is compatible with housings of various sizes and configurations.